Mukesh Ambani, India’s richest man, is the biggest loser among the country’s billionaires as the rupee’s slump to record lows erased 24% of his fortune.

The chairman of Reliance Industries Ltd., operator of the world’s biggest oil refinery complex, has lost US$5.6-billion of his wealth since May 1, as the rupee’s plunge accelerated. The 56-year-old is left with a net worth of US$17.5-billion, according to the Bloomberg Billionaires Index.

The Indian rupee is the worst-performing major currency in the world in the past month, coming under pressure as international investors sold emerging-market assets amid concern the U.S. will pare its US$85-billion monthly stimulus. The value of holdings by India’s billionaires are worth less in dollars as the rupee declined and foreign investors sold shares in large-cap companies, said Munesh Khanna, a senior partner at Grant Thornton LLP in Mumbai.

“There is irrationality; the rupee is weak and will go down further,” Khanna said. “Foreign institutional investors are invested in the larger-cap companies and are pulling out money from India. That is putting a lot of pressure on those companies.”

International investors have sold a net US$3-billion of Indian stocks since June 3, according to the nation’s Securities & Exchange Board. The S&P BSE Sensex index declined 1.9% to 17,905.91 Wednesday, extending its four-day drop to 7.6%, the most since July 2009. The rupee also extended its slide Wednesday, touching an all-time low of 64.55 per dollar.

Anil Ambani, the younger brother of Mukesh, has lost 17%, or US$1.3-billion, of his net worth since May. Ambani, 54, has a fortune of US$6.3-billion and is the country’s eighth-richest man, according to the Bloomberg ranking. The majority of his wealth is derived from stakes in publicly traded companies, including Reliance Communications Ltd., India’s third-largest mobile-phone company by market value.

Reliance Communications reported earlier this month first- quarter profit that missed analysts’ estimates after finance costs increased because of the rupee’s weakness against the dollar. Net income fell 33% to 1.08-billion rupees (US$16.7-million) in the three months ended June from a year earlier, its 15th drop in profit in 16 quarters.

“Companies with large foreign-currency debt will feel the pressure and their valuations will come down,” Khanna said.

Refining Oil

Shares of Reliance Industries, Mukesh Ambani’s most valuable asset, declined about 15% from its 2013 peak on July 19 through Wednesday. Reliance Industries’ profit beat analyst estimates for the fifth straight quarter as the rupee’s plunge boosted dollar-denominated earnings. Net income rose 19% to 53.5 billion rupees in the three months ended June 30 from a year earlier, the Mumbai-based company said last month.

Much of the output from Reliance’s two refineries at Jamnagar in the western state of Gujarat is exported and sold in the U.S. currency. A stronger dollar increases Reliance’s earnings in rupees.

Dilip Shanghvi, the founder of Sun Pharmaceutical Industries Ltd., India’s biggest drug maker by market value, has shed US$2-billion in net worth since May, the second-biggest loser among Indian billionaires. The 58-year-old has a fortune of US$10.2-billion, according to the Bloomberg index. Shares of Sun Pharmaceutical fell 16% from a record on July 30 through Wednesday.

Buying Debt

Kumar Mangalam Birla, the 46-year-old chairman of Aditya Birla Group, has lost about US$950-million, or 11%, of his net worth since May, according to the index. Shares of Aditya Birla Nuvo Ltd., his most valuable asset after iron-ore miner Essel Mining & Industries, plunged 17% from Aug. 14 through Wednesday.

The Reserve Bank of India said Aug. 20 it will start buying government debt to pump funds into markets and consider reducing weekly sales of cash-management bills to rein in a surge in bond yields that threatened the economy. The central bank engineered a cash crunch in Asia’s third-largest economy last month to shore up the rupee.

The Bloomberg Billionaires Index is a dynamic measure of the world’s wealthy based on changes in markets, the economy and Bloomberg reporting. Each net worth figure is updated every business day at 5:30 p.m. in New York. Stakes in publicly traded companies are valued using the share’s most recent closing price. Valuations are converted to U.S. dollars at current exchange rates.